The present invention relates to a coffee-making device, comprising a housing with a cylinder in which a piston is provided, for compressing with the piston coffee placed on said piston, said piston being movable by means of a drive mechanism, and said drive mechanism being provided in said housing, and comprising a cover that can be placed on said cylinder, in order to bound a compression chamber with said cylinder and piston, means for introducing water into the compression chamber, means for discharging brewed coffee from the compression chamber, and means for removing the compressed coffee tablet, said movable cover comprising a swivelling arm structure, which is rotatable substantially about and over said cylinder in such a way that said cover can be moved above and away from the end of the cylinder, in order to bring said cover into engagement in a sealing manner with said cylinder end, said drive mechanism being designed to operate both said piston and said swivelling arm, and comprising a rotary input shaft.
Such a coffee-making device is known from European Patent Application 1005821, which was published after the priority date of the present application. The European application discloses a first embodiment of a coffee-making machine which operates without piston and a second embodiment with piston, the piston being made reciprocating by a gearwheel provided with screw thread. This means that a separate device for generating fluid pressure must be present, with the result that the device becomes complicated and takes up a large amount of space.
Such a design means that with uniform rotation of the drive motor the piston will carry out a uniform motion.
In the prior art coffee-making devices in which the motion of the piston is carried out by means of a crankshaft-cum-piston/cylinder structure are known, in the case of which devices the coffee is placed on the piston and, after the coffee has been compressed, water is forced through the coffee. An example of such a structure is found in U.S. Pat. No. 5,638,739. After the coffee has been consumed, the pressed coffee tablet is driven out of the cylinder and removed. This is carried out in U.S. Pat. No. 5,638,739 by means of a swivelling arm structure which by means of a complicated gearwheel system runs synchronously with the motion of the crankshaft and piston. By means of this swivelling arm structure, the coffee tablet is swept off the top side of the cylinder.
A complicated mechanism comprising a further slidable cylinder is used to close off the top side of the cylinder.
A coffee-making device operating with a piston is known from U.S. Pat. No. 5,622,099A. The piston is moved up and down by means of an operating lever fitted on the top side of the coffee-making device. Such a device is not suitable for use in automatically operating coffee-making devices.
EP0380450A discloses a structure in which the cylinder is not immovable connected to the housing, but can be tilted around it, and in which the piston is moved in a certain tilted position.
It is the object of the present invention to simplify a coffee-making device of the type described above considerably by substantially reducing the number of components used for it.
This object is achieved in a coffee-making device of the type described above in that said drive mechanism for said piston is provided with means for converting a uniform rotating motion into a non-uniform reciprocating motion.
The closing and opening characteristic of the piston in the cylinder unit can be influenced, in other words optimized, by converting the uniform rotating motion of the drive motor into a non-uniform motion.
Such a non-linear motion characteristic of the piston can be obtained in any way known in the prior art. An example that can be mentioned is a curved disc which is driven by the rotary motor and in turn drives the piston. A certain opening and closing characteristic of the piston can be obtained through the special shape of the curve.
Another possibility is to use a crankshaft structure.
In this way a particularly compact structure can be obtained with a single drive motor. More particularly, the actual coffee-making process can be carried out irrespective of the coffee material, or the quantity of coffee material can be varied, without special measures as regards structure being necessary. A particularly simple structure can be obtained by using a swivelling arm structure for moving the cover on the cylinder. Owing to the fact that the swiveling arm rotates substantially about the axis of the crankshaft, a particularly compact device is obtained.
Such a swivelling arm structure can be driven in any way known in the prior art. However, it is preferably driven by the crankshaft. If the structure is designed in a suitable manner, it is possible for it to be driven directly by the crankshaft, in other words without interposing gearwheels and other transmission mechanisms.
The reciprocating motion of the rocker arm in order to place the cover on the free end of the cylinder in a sealing manner can also be carried out in any way known in the prior art. It is, however, preferably carried out by means of a cam/cam follower mechanism. Said cam/cam follower mechanism is preferably likewise fitted on the crankshaft of the piston. By this measure also, further simplication of the coffee-making device according to the invention can be obtained. The coffee-making device can consequently be manufactured more cheaply, and fewer components will wear, and any parts that may have worn will be easier to replace. Cleaning can also be carried out in a simple manner.
The structure described above works in particular if the crankshaft rotates in different directions, in other words if it does not rotate in only one direction during a coffee-making operation. In particular, if a combination with cams/cam followers is envisaged for driving the swivelling arm structure, such a motion in different directions is advantageous. Of course, a corresponding, suitable control is present.
Certain parts of the motion process of the swivelling arm structure can be controlled by means of a spring or the like.
According to an advantageous embodiment of the invention, a valve with variable restriction is present in the outlet for the brewed coffee. The valve structure is designed in such a way that at relatively low pressure a relatively large passage is present. If the pressure increases, the passage will become smaller.
In this way it is possible, without further mechanical components and/or controls, to build up a higher back pressure in the coffee depending on the pressure of the water moving through the coffee. In this way, the back pressure of the water in the coffee can be determined, controlled purely by the inlet pressure of the water in the coffee. This makes it simple to make xe2x80x9cordinaryxe2x80x9d coffee or espresso coffee, or variants of these.
It will be understood that the valve structure just described can likewise be used in combination with other coffee-making devices known from the prior art. The fact is that this valve structure is fully independent of the remainder of the coffee-making devices. Of course, it is the case that the already simple structure of the coffee-making device is further simplified by using such a valve.